This was fun (I always say that). I talked via telephone bridge, with John Blackham, N7TEK, Doug Brewer, and Kip Buckner, KC7OXX, about a project called On Target. This program is affiliated with the Boy Scouts. Among other things, they get the Scouts to climb mountains and signal each other with very high frequency light in the 500 nM wavelength. OK, they use reflected sunlight, with signal mirrors. But ham radio has been an integral part of on-site coordination, in order to make sure that people are looking the right diretion for the flashes of light.
Question for you: how far do you think it's possible to send a message using a signal mirror? One mile? Five miles? Ten? The answer is in this podcast.
On Target main page is http://www.ontargetbsa.org and has plenty of great links